Installing Reverse Osmosis System

This post is the ultimate guide to installing a reverse osmosis system by yourself with clear diagrams and a step-by-step trouble-free way of how you can set up your RO system.

Therefore, whether you’ve got a countertop, under the sink, or whole house RO system, or you are planning to get one, this guide will certainly come in handy in ensuring your system is installed properly for optimum performance.

Reverse Osmosis Installation

Almost all RO systems require some degree of installation. However, given that there are several different kinds of RO systems out there, one installation procedure may not work for all.

From countertop systems to under-the-sink units to whole-house systems, each of these types of RO systems has its own setup procedure and a number of different parts to put together.

If you don’t know how to go about it, it can be somewhat challenging and frustrating at the same time. Furthermore, without the right skills or being a trained plumber, installing reverse osmosis systems like a commercial or whole house RO system is quite hard.

How to install an under-sink RO system

Under-sink reverse osmosis systems are typically designed to be installed beneath a kitchen counter, sink, or basement.

These units often consist of four to five different filtration canisters plus a storage tank for holding the purified water and a countertop spigot that’s separate from the kitchen faucet for delivering the filtered water when needed.

The installation of an under sink RO system is a bit complicated compared to the countertop RO system but it’s fairly straightforward provided you follow the installation manual provided correctly.

The following is the most complete diagram of a typical reverse osmosis system.

reverse osmosis plumbing diagram
Reverse osmosis system – plumbing diagram

DIY Installation Steps

The first thing you should do is to remove all the components and confirm that all the parts that are necessary to complete the installation are present.

Your new system should have the following items:

  • The RO filters both prefilters and post-filters plus their housings
  • The RO membrane
  • The RO storage tank plus its stand 
  • The faucet
  • The tubings
  • The drain saddle
  • The tank valve
  • Feedwater adapter

Apart from the items listed above, you will also need the following tools during the installation process:

  • Housing wrenches both for the filters and the membrane (sizes 5/8”, 9/16”, ½” & 7/16”)
  • Teflon tape
  • Phillips head screwdriver
  • Drill bits for the faucet mounting hole (sizes 1¼”, ½” & ¼”)
  • Plastic tubing cutter

For convenience purposes, it may be advisable to find a suitable location where you are going to install the system prior to beginning the actual installation.

Ensure there’s plenty of space under the counter or sink for proper installation. You want to install the system close to the cold water line and the sink drainpipe.

The following guidelines are for installing a reverse osmosis system. The model we’ve used is the iSpring RCC7 RO system.

Prefilters, RO Membrane and Tank Pre-installation

We would recommend you begin the installation by first setting up your RO unit before connecting and installing the other components.

Prefilters Installation Procedure

  • Insert the prefilters into their respective housing starting with the first stage filter which is the sediment filter.
  • Ensure the O-rings are perfectly seated inside the housing.
  • Align the filters into the housing correctly while as you attach them into the RO system.
  • Screw the housing into the system. You want them to fit snug, so don’t over-tighten the housing while screwing them.

The RO Membrane Installation Procedure:

  • The next step is to install the RO membrane. Remove the tubing going into the membrane housing. Remove the membrane housing cap.
  • Ensure the O-ring is on the edge of the membrane housing always. It should not be in the cap.
  • Remove the RO membrane from its packaging and insert it into the housing (the iSpring RCC7 membrane has one end with two O-rings). These two O-rings should go first into the membrane housing.
  • After setting the membrane properly inside its housing, screw the cap back on the membrane housing.

The RO Storage Tank Installation Procedure:

  • Wrap the RO tank thread with Teflon tape and screw the tank valve on it.
  • Ensure it is aligned right and screw it on the thread good but don’t overtighten it (should only be hand tighten)

Cold Water Line Connection

  • Shut off your cold water supply via the angle stop shut-off valve located under the sink or the place where you are going to install the system.
  • Once you shut off the water supply, then relieve the pressure in the line by opening your cold water faucet.
  • Now using an adjustable wrench, the next step is to disconnect the water line or rather the riser tube from your existing cold water shut-off valve.
  • Move the riser tubing away from the shut-off valve to create room for the feed water adapter which in this case is the iSpring AFW43 feed water adapter.
  • Put Teflon tape on the top seal of the adapter as well as on the threads of the existing cold water shut-off valve to ensure a secure connection and to prevent leaks.
  • Screw in the feed water adapter to the thread of the shut-off valve (should only be hand tightened)
  • Reconnect the riser tube to the adapter such that it sits between the shut-off valve and the bottom part of the riser tube. Tighten with a wrench to ensure a secure connection. 
  • The adapter features a built-in shut-off and it forms the feed water supply connection for the RO system.

Drain Line Connection

  • The next vital connection in the RO system installation is the RO wastewater connection to the drain line under the sink which involves attaching a drain saddle connector.
  • Position the drain saddle approximately 6” above the trap and mark for the opening.
  • Drill the drain hole at the selected point through one side of the pipe. The hole should be a little bit bigger than ¼” in diameter, preferably 5/16” in order to get the tubing in.
  • Add the drain pad positioning it such that the opening aligns with the hole you’ve drilled.
  • Now attach the two halves of the drain saddle on the drainpipe while positioning them so that the opening aligns well with the drilled hole.
  • Use a drill bit or punch to verify that the drain saddle is properly aligned. Secure the saddle clamp on the pipe with the bolts and nuts provided.
  • Ensure not to over tighten the drain saddle clamp. There should be equal space between the saddle halves on both sides.

Faucet Installation

When it comes to faucet installation, you will need to consider the type of sink you have first and whether or not it already has a faucet-mounting hole already installed.

If your sink already has a hole installed, then remove the cover and proceed with the mounting procedure in step 2. However, if it comes with no pre-installed hole, then drilling is required to accommodate the RO faucet.

Step 1: Drilling the Faucet-mounting Hole

Procedure for porcelain, enamel, cast iron, or ceramic on metal sink:

  • First, ensure there’s an ample flat area for the faucet base so that the drill does not interfere with anything below and the base nut can easily be tightened properly. A 2” flat surface is sufficient. It shouldn’t exceed 1¼” thickness.
  • To make the mounting hole, mark the center using a center punch for a ¼” pilot hole.
  • Carefully drill the ¼” pilot hole through the porcelain with masonry drill bit using light pressure and slow speed, and stop as soon as the metal surface shows.
  • Change the drill bit to the standard metal cutting bit and continue drilling through the metal just below the porcelain surface.
  • Enlarge the pilot hole using both a larger masonry and metal drilling bits until it is ½” in diameter. Clean up sharp edges if there are any.
  • You must be cautious when penetrating the porcelain sink through to the metal base to prevent chipping or scratching.

Procedure for stainless steel sinks:

  • Like porcelain and other types of sinks, ensure there’s at least 2” flat area below for the faucet base.
  • Mark the center using a center punch for where you are to drill the ¼” diameter pilot hole.
  • Carefully drill the ¼” hole through the metal sink.
  • Change the drill bit to a larger one and enlarge the hole until it is ½” in diameter.
  •  Lightly file sharp edges of the hole to ensure it is smooth without any burrs.

Step 2: Installing the RO Faucet

Procedure for installing a standard non-air gap RO faucet:

  • Disassemble all the hardware from the threaded shank.
  • Slide up the chrome base plate and the rubber washer base (if provided) on to the shank of the faucet body
  • Insert the feed threaded shank or the stem of the faucet through the drilled sink hole, then orient the faucet.
  • Ensure the faucet body, base plate and the rubber washer are properly in place above the sink.
  • From below the sink, slide up the gasket or the star lock washer provided over the threaded faucet shank.
  • Next slide the hex nut over the faucet shank under the sink
  • While making sure the faucet is positioned in the right spot you want it to be, tighten the nut firmly with hand or a wrench to ensure it’s well secured in place.
  • Go back up to the top and check that the faucet is properly aligned in the desired position.
  • If it turned a little bit while tightening it, then you may need to loosen it and rotate it to the right direction and firmly tighten the nut again from underneath the sink.
  • Ensure the faucet is positioned such that it empties into the sink. Plus the spout should be able to swivel freely for convenience.

Procedure for installing an air gap faucet:

Some states require air gap faucets when installing an RO system. Therefore, you need to check your local plumbing code to ensure compliance.

Unlike the non-air gap faucet, installing an air-gap faucet is slightly different since it comes with two additional barbed fittings.  In addition, non-air gap faucets need a 1¼” hole in the sink unlike the ½” hole for the standard faucet.

To make this hole you will require special tools like a Relton cutter for porcelain sinks or chassis punch for stainless steel sinks.

  • Using a center punch mark the center where you are going to drill the hole if a large enough mounting hole is not already available
  • With the chassis punch or the Relton cutter, drill the 1¼” hole through the sink.
  • File any sharp edges of the hole to ensure it is free from any burrs.
  • Now slide the chrome base plate on to the faucet stem aligning it with the barbed fittings. Next slide the rubber washer under the base plate.
  • Slide the faucet through the drilled hole and from below the sink, slide up the metal washer followed by the air gap washer.
  • Next slide up the lock washer under the air-gap washer.
  • Finally, take the hex nut and tighten it all the way up to the lock washer to secure the faucet.

RO Tubing Connection

Now that everything is set, the next step is to attach the tubings to the RO system.

Procedure for RO systems with non-air gap faucet:

  • First, connect the red tubing to the first stage filter (sediment filter) and then connect it to the feed water adapter you’ve installed on your cold water line.
  • Connect the blue tubing (pure water line) to the post-filter going to the faucet.
  • Screw one end of the quick connect fitting provided onto the faucet stem and attach the other end of the blue tubing to the other end of the fitting. Use Teflon tape on the stem thread to ensure a secure connection and prevent possible leakages.
  • Connect one end of the yellow tubing to the post-carbon filter and the other end to the RO tank valve.
  • Attach the black tubing (waste water line) to the flow restrictor on the RO unit and then connect the other end directly to the drain saddle assembly installed on your sink drain pipe.
  • Ensure all inserts, ferrules and sleeves provided for the installation are used.

Procedure for RO systems with air gap faucet:

  • Start by getting the blue line connection on. Slide the fastener (brass nut) followed by the olive onto the out the outside of the tubing and fit the sleeve into the end.
  • Insert the end of the tubing that has the sleeve into the end of the faucet stem making sure the tubing fits all the way in. Slide the olive and fastener up and secure the tube in place.
  • Alternatively, you can use a quick-connect fitting provided to connect the tubing into the faucet. Wrap the faucet stem thread with Teflon tape to ensure a secure connection.
  • Screw one end of the fitting onto the faucet stem and attach the end of the ¼” blue line on to the bottom of the stem making sure it fits all the way in.
  • Once the blue line is connected, next is the drain line connection. Attach the ¼” black tubing from the RO system onto the smaller diameter barbed fitting in the faucet base which is the drain input.
  • Finally, attach the 3/8” black line onto the larger diameter barbed fitting which is the drain output going into the sink drain pipe. Connect the other end of the tube to your drain saddle. Ensure it runs straight downhill to the drain saddle.

Note: The color of the lines may slightly vary from manufacturer to manufacturer, but the ones we’ve used in describing the tubing connection procedure above are industry standard colors.

System Hook Up

Depending on the location of the supply tank, the RO unit can be mounted either to the left or right sink cabinet sidewall. In general, the unit should be at the front while the tank should sit at the rear of the cabinet.

  • To mount the unit, you need to elevate it about 2” off the floor, then level it and mark the exact location of the mounting holes needed.
  • Next drill the hole for the mounting screws. Install the screws as you allow the mounting bracket slots to slide over them.
  • If your cabinet sidewalls are not that solid, you can set the unit on the floor and use the screws to secure it against the cabinet wall in a vertical position.
  • Once you are done, double-check all your fittings to make sure they are tight and that the tubings are secure in the fittings.

Starting Up the System

  • First, turn off the RO storage tank shut-off valve to prevent water from entering the tank.
  • Turn on the feed water supply valve on your cold water supply line. Check around the valve for any leaks. If you detect any leaks, turn off the supply valve and make the necessary repairs.
  • Open your installed RO faucet on the sink and give it some time to allow the water to drip. It may approximately 10 minutes before the water starts dripping from the faucet.
  • When the water starts dripping, allow it to run for 10 to 15 minutes to flush the pre-filters and the post-filters. The initial water produced may be black in color and shouldn’t be consumed.
  • Now close the faucet and open the shut-off valve on the storage tank to allow water to fill the tank. During this time, double-check all the fittings to ensure that there are no leakages and make necessary corrections if there are any.
  • Once the tank is filled, open the faucet and then drain the RO system completely. Shut off the faucet and allow the tank to refill.

You might want to drain the system at least 3 times prior to use.

In most cases, the RO system you will get will come with all the installation instructions but if it’s not provided or you are just want to know how an RO system is installed, then our complete installation guide above can be of great help.

You can also check this sample video on iSpring RCC7 RO system installation for a better perspective.

Hiring a Professional Plumbing Service

As you’ve seen above, an RO system is a bit complex and not everyone might feel comfortable installing it DIY-style. It may be quite confusing and can take some time if you are not that familiar with the system.

If you are worried that you don’t have the right background knowledge, tools, or time to install it yourself, then we’d recommend having a professional plumber do the installation for you.

However, when it comes to hiring a professional plumber, you need to factor in the cost and ensure you pick a good local plumbing service that will deliver.

To get a much clear understanding of the cost of hiring a professional plumber to install an RO system refers to our RO cost article for more details.

If you don’t have a local plumber whom you know well and trust, then visit the Home Advisor, enter your Zip code to find a good suggestion with an estimation cost.


Reverse osmosis installation cost estimation

How to install a countertop RO system

A countertop RO system basically consists of a portable reverse osmosis filter which is meant to be installed on the countertop of any kitchen or bathroom sink to help purify the drinking water.

It’s an ideal solution for people living in apartments where you are not allowed to perform permanent modifications to the kitchen sink counter or the drain system.

A countertop RO system can work with most basic faucets and the installation is quite simple. It’s a typical DIY process that most people can manage to do by following the manual provided.

Below is a step by step procedure you can follow to easily install a countertop RO system to any standard faucet.

  • Start by removing the aerator from your kitchen faucet
  • Attach the diverter valve to the exposed faucet thread and then hand tighten it.
  • If the diverter doesn’t fit in your faucet right away, you may need to use an adapter if it’s provided.
  • Attach the diverter to the adapter and then attach it to the faucet. You can use Teflon or plumber tape to ensure the connection is well fixed.
  • Make sure the lever that’s on the diverter is horizontal. Open cold water and let it run for a moment to let the stale water out while checking for leaks.
  • Now remove the red cap from the drinking water tube and insert it a glass or any other container and flip the diverter’s lever and let the water to go through the RO system and flow through the drinking tube.
  • It may take a moment for the system to produce pure water, so give it sufficient time. Once it’s done filling up the container, switch the diverter back to faucet and your system is now ready for use.

Alternatively, you can check out this sample video on installing an APEC countertop RO system to get a much better picture of how to carry out the installation of a countertop RO system.

How to install a whole house or commercial RO system

While a standard RO system is fairly easy to install, whole house or commercial RO systems are a bit more difficult when it comes to installing them.

However, this shouldn’t deter you from having one installed with the assistance of a professional. The good thing though is that most whole house or commercial RO systems come with special services from the supplier including installation. 

Installation cost (for The USA customers)

As we mentioned earlier, how much the installation of a new RO system will cost depends on the kind of system you want to install.

For standard under-sink systems, the cost of outsourcing the services of a professional plumber should range anywhere between $150 and $400 USD. It can go up to $500 USD in special cases.

When it comes to whole house RO systems, it may be somewhat difficult to estimate the cost as they are often more complex plus the price may vary from one supplier or plumbing service provider to another. The bare minimum is probably $500 USD and it can go up to $1000 USD.

Reverse osmosis system maintenance

Whether you are installing a standard or whole house RO system, proper maintenance is paramount to ensure optimum performance of the system.

For standard under sink RO systems, the maintenance mainly involves the replacement of the filters and the RO membrane.

The filters need to be changed on time otherwise your water supply and quality can be affected. Refer to our RO membrane and filter cartridges replacement article for more information on when and how to change the filters and the membrane.

Apart from the periodic replacement of the filters and the membrane, you may need to change the other parts of your RO system periodically or in case of failure.

These parts include the faucet, RO storage tank, shut-off valves, and booster pump. Our RO tank, RO faucet, and RO booster pump articles cover these parts.

They are worth a look to get a much better insight to help you understand these RO parts and how to go about their maintenance.

In short, the only way to maintain an RO system and make sure it’s in its best condition is to ensure you never skip any filter replacements and to constantly inspect the other parts to confirm they are functioning as expected. You should stay on top of any maintenance task.


Installing a reverse osmosis system is the best thing you can do to ensure your household gets clean and healthy drinking water throughout. The installation may be a bit hard and time-consuming but it’s definitely worth it.

With a little technical skill, preparation, and all the necessary tools, it’s fairly not that challenging to pull off. Furthermore, in most cases, the new RO system will include clear and precise installation instructions.

In the event it’s not enough or the package does not come with the installation instructions, our guide above should be very useful.

However, keep in mind that the individual steps may vary slightly depending on the type of system you get and your specific plumbing setup. They are basically general guidelines.

Therefore, make sure to refer to the manufacturer manual for your specific model before proceeding with the installation if you are doing it yourself, or hire a professional plumber if you feel you may not be able to install it correctly.

For a whole-house RO system, it’s best to confirm with the supplier if they offer installation services to get an estimate of the cost. You want too to make sure the installation is done in accordance with your state or local plumbing codes.

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